Truing MV vs. BC

Skookum

Flattus Domini
May 6, 2017
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Does the wind speed and direction need to be recorded in the ballistics app/software when truing the speed and the bc? Thanks.
The prudent answer is "yes".

Whether it makes a real difference or not would depend on the actual wind speed and direction you are experiencing.
 
Apr 24, 2017
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Does the wind speed and direction need to be recorded in the ballistics app/software when truing the speed and the bc? Thanks.
The short answer is “yes” (the wind at your position NOT Wind at Target)

Also verify and enter the direction of fire (Target azimuth)
 
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BLKWLFK9

come at me bro
Feb 13, 2017
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I've personally experienced the need to true at 1k. I trued out to 800, every thing was spot on other than 1k. I think I was .2 or .4 MIL low at 1k where everything else lined up great. I then trued at 1k, got it nailed, and wawas only off by .1 on shorter ranges. Instead of truing at 500 and truing bc at 800, I just used my actual velocity and trued bc, then changed my velocity a hair to get the final touch up.
Im doping out some new ammo on thur. I'm going to try the 500 then 800 method.
 
Apr 24, 2017
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I don't know how you would true at 800 with BC when it comes up 4.8 mils with either one listed. If they are the same, what are you truing?

I re-ran it with all the inputs on JBM, exactly as listed on the JBM table shown in post #58. At 800 yards, with the listed speed of 2900fps and all other inputs identical, It is 4.8 mils with a .583 G1 and 4.8 mils with a .595 G1.

So, near as I can figure, Frank had to be talking about the rest of the trajectory.
I'm not sure where .595 G1 came from but this was what I got using other software and the inputs supplied

Cold Bore Desktop *AJ off *no azimuth supplied

AB G7 .294
800=4.8 1000 = 6.9 1350=11.7 1500 =14.2

AB G1 .575
800=4.9 1000 = 7.1 1350=12.0 1500 =14.6

Prime G7 .289
800=4.9 1000 = 7.0 1350=11.8 1500 =14.4

Prime G1 .583
800=4.9 1000 =7.0 1350=11.9 1500 =14.5

using the modified G1 BC .595 lined up at 800
800=(4.8) 1000 =(7.0) 1350=11.7 1500 =14.2

using modified G1 BC .610 lined up at 1350
800=(4.8) 1000 =(6.9) 1350=11.5 1500 =13.9

using modified G7 BC .302 lined up at 1350
800=(4.8) 1000 =(6.9) 1350=11.5 1500 =13.9

TRASOL (Cold Bore Engine) *no azimuth supplied

AB G7 .294
800=4.82 (4.8) 1000 = 6.93 (6.9) 1350=11.71 (11.7) 1500 =14.17 (14.2)

AB G1 .575 lined up at
800=4.88 (4.9) 1000 = 7.06 (7.1) 1350=12.0 (12.0) 1500 =14.6 (14.6)

Prime G7 .289
800=4.85 (4.9) 1000 = 6.99 (7.0) 1350=11.84 (11.8) 1500 =14.37 (14.4)

Prime G1 .583
800=4.86 (4.9) 1000 =7.01 (7.0) 1350=11.89 (11.9) 1500 =14.43 (14.5)

using the modified G1 BC .595 lined up at
800=4.82(4.8) 1000 =6.94 (6.9) 1350=11.73 (11.7) 1500 =14.19 (14.2)

modified G1 BC .612 lined up at 1350
800=4.77 (4.8) 1000 =6.85 (6.9) 1350=11.53 (11.5) 1500 =13.88 (13.9)

modified G7 BC .302 lined up at 1350
800=4.77 (4.8) 1000 =6.85 (6.9) 1350=11.52 (11.5) 1500 =13.87 (13.9)

Applied Ballistics (Kestrel 5700 Elite) *AJ off (WS2) *no azimuth supplied DOF=000

AB CDM (Norma 130 Diamond)
800=4.80 (4.8) 1000 = 6.89 (6.9) 1350=11.50 (11.5) 1500 =13.95 (14.0)

AB G7 .294
800=4.81 (4.8) 1000 = 6.90 (6.9) 1350=11.48 (11.5) 1500 =13.91 (13.9)

AB G1 .575
800=4.85 (4.9) 1000 = 6.96 (7.0) 1350=11.60 (11.6) 1500 =14.04 (14.0)

Prime G7 .289
800=4.84 (4.8) 1000 =6.95 (7.0) 1350=11.61 (11.6) 1500 =14.09 (14.1)

Prime G1 .583
800=4.82 (4.8) 1000 =6.92 (6.9) 1350=11.49 (11.5) 1500 =13.89 (13.9)

*using modified G1 BC .595 lined up at 800
800=4.78 (4.8) 1000 =6.85 (6.9) 1350=11.34 (11.4) 1500 =13.68 (13.7)

Ballistic AE (JBM engine) *no azimuth supplied

AB G7 .294
800=4.81 (4.8) 1000 = 6.91 (6.9) 1350=11.51 (11.5) 1500 =13.95 (14.0)

AB G1 .575
800=4.85 (4.9) 1000 = 6.97 (7.0) 1350=11.62 (11.6) 1500 =14.07 (14.1)

Prime G7 .289
800=4.85 (4.9) 1000 =6.97 (7.0) 1350=11.64 (11.6) 1500 =14.14 (14.1)

Prime G1 .583
800=4.82 (4.8) 1000 =6.92 (6.9) 1350=11.52 (11.5) 1500 =13.93 (13.9)

*using the modified G1 BC .595 lined up at 800
800=4.79 (4.8) 1000 =6.86 (6.9) 1350=11.36 (11.4) 1500 =13.68 (13.72)
 
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Skookum

Flattus Domini
May 6, 2017
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Your mom's
I'm not sure where .595 G1 came from but this was what I got using other software and the inputs supplied

Cold Bore Desktop *AJ off *no azimuth supplied

AB G7 .294
800=4.8 1000 = 6.9 1350=11.7 1500 =14.2

AB G1 .575
800=4.9 1000 = 7.1 1350=12.0 1500 =14.6

Prime G7 .289
800=4.9 1000 = 7.0 1350=11.8 1500 =14.4

Prime G1 .583
800=4.9 1000 =7.0 1350=11.9 1500 =14.5

using the modified G1 BC .595 lined up at 800
800=(4.8) 1000 =(7.0) 1350=11.7 1500 =14.2

using modified G1 BC .610 lined up at 1350
800=(4.8) 1000 =(6.9) 1350=11.5 1500 =13.9

using modified G7 BC .302 lined up at 1350
800=(4.8) 1000 =(6.9) 1350=11.5 1500 =13.9

TRASOL (Cold Bore Engine) *no azimuth supplied

AB G7 .294
800=4.82 (4.8) 1000 = 6.93 (6.9) 1350=11.71 (11.7) 1500 =14.17 (14.2)

AB G1 .575 lined up at
800=4.88 (4.9) 1000 = 7.06 (7.1) 1350=12.0 (12.0) 1500 =14.6 (14.6)

Prime G7 .289
800=4.85 (4.9) 1000 = 6.99 (7.0) 1350=11.84 (11.8) 1500 =14.37 (14.4)

Prime G1 .583
800=4.86 (4.9) 1000 =7.01 (7.0) 1350=11.89 (11.9) 1500 =14.43 (14.5)

using the modified G1 BC .595 lined up at
800=4.82(4.8) 1000 =6.94 (6.9) 1350=11.73 (11.7) 1500 =14.19 (14.2)

modified G1 BC .612 lined up at 1350
800=4.77 (4.8) 1000 =6.85 (6.9) 1350=11.53 (11.5) 1500 =13.88 (13.9)

modified G7 BC .302 lined up at 1350
800=4.77 (4.8) 1000 =6.85 (6.9) 1350=11.52 (11.5) 1500 =13.87 (13.9)

Applied Ballistics (Kestrel 5700 Elite) *AJ off (WS2) *no azimuth supplied DOF=000

AB CDM (Norma 130 Diamond)
800=4.80 (4.8) 1000 = 6.89 (6.9) 1350=11.50 (11.5) 1500 =13.95 (14.0)

AB G7 .294
800=4.81 (4.8) 1000 = 6.90 (6.9) 1350=11.48 (11.5) 1500 =13.91 (13.9)

AB G1 .575
800=4.85 (4.9) 1000 = 6.96 (7.0) 1350=11.60 (11.6) 1500 =14.04 (14.0)

Prime G7 .289
800=4.84 (4.8) 1000 =6.95 (7.0) 1350=11.61 (11.6) 1500 =14.09 (14.1)

Prime G1 .583
800=4.82 (4.8) 1000 =6.92 (6.9) 1350=11.49 (11.5) 1500 =13.89 (13.9)

*using modified G1 BC .595 lined up at 800
800=4.78 (4.8) 1000 =6.85 (6.9) 1350=11.34 (11.4) 1500 =13.68 (13.7)

Ballistic AE (JBM engine) *no azimuth supplied

AB G7 .294
800=4.81 (4.8) 1000 = 6.91 (6.9) 1350=11.51 (11.5) 1500 =13.95 (14.0)

AB G1 .575
800=4.85 (4.9) 1000 = 6.97 (7.0) 1350=11.62 (11.6) 1500 =14.07 (14.1)

Prime G7 .289
800=4.85 (4.9) 1000 =6.97 (7.0) 1350=11.64 (11.6) 1500 =14.14 (14.1)

Prime G1 .583
800=4.82 (4.8) 1000 =6.92 (6.9) 1350=11.52 (11.5) 1500 =13.93 (13.9)

*using the modified G1 BC .595 lined up at 800
800=4.79 (4.8) 1000 =6.86 (6.9) 1350=11.36 (11.4) 1500 =13.68 (13.72)
.583 came from Frank's written dope sheet in post #58, .595 came from the BC Frank put into JBM. It is listed clearly at the top of the data.
 
Apr 24, 2017
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.583 came from Frank's written dope sheet in post #58, .595 came from the BC Frank put into JBM. It is listed clearly at the top of the data.
I'll clarify. I meant I didn't know how he came up with .595 (I thought he might have been setting coldbore to = 4.8 at 800)
you had pointed out that both .583 and .595 = 4.8 at 800 in JBM so I had included both in my examples
 
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Skookum

Flattus Domini
May 6, 2017
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943
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Your mom's
I'll clarify. I meant I didn't know how he came up with .595 (I thought he might have been setting coldbore to = 4.8 at 800)
you had pointed out that both .583 and .595 = 4.8 at 800 in JBM so I had included both in my examples
My contention was that Frank wasn't truing his data at 800 at all but at some further distance, and .595 accomplished that. Regardless, truing at 800 makes no sense if both BC's give the same result.

I confined myself to JBM since that is what was used in his example.
 
Apr 24, 2017
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My contention was that Frank wasn't truing his data at 800 at all but at some further distance, and .595 accomplished that. Regardless, truing at 800 makes no sense if both BC's give the same result.

I confined myself to JBM since that is what was used in his example.
I agree. Truing at 800 yards makes no sense if both BC’s give the same result

If “800 yards” is the set “calibration point” then that presupposes the shooter hasn’t got access to ranges beyond the “calibration point” to even know if the trajectory is off at further distances and if he (the shooter) has “1350 yards” set as the “calibration point” then the shooter has access to the range necessary (based on the current example given) to true both the BC and back-extrapolate the MV
 
Jul 2, 2014
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London, KY
So I was stressing over dope for an upcoming match. Literally only got to put 2 rounds on steel at 993 yards before a downpour the last chance I had to collect data. Following the advice here, I input my MV from my Magnetospeed and tweaked the BC until my 500, 800, and 1,000 (993) yard dope matches what I observed from the 1,000 yard shot.

Using Shooter I put together a dope card that allowed me to get first round hits out to 1,207, along with my fiancé who shot her first match and did excellent. End result was a solid 2nd in my 2nd match.

Thank you all a lot for the help.
 

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DocUSMCRetired

Applied Ballistics
Apr 16, 2014
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www.appliedballisticsllc.com
The short answer is “yes” (the wind at your position NOT Wind at Target)

Also verify and enter the direction of fire (Target azimuth)
It is actually more complicated than that. This is why our AB Analytics allows for wind in 3D in 10 different places. We can place special monitors that measure the wind in all directions and report in real time. This is how we validate the accuracy of the solver. By using a dozen or sometimes more instruments at one time to remove the variables. The wind everywhere technically matters. But by how much can differ greatly.

http://appliedballisticsllc.com/Articles/NVDOC1403-Wind.pdf
 
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DocUSMCRetired

Applied Ballistics
Apr 16, 2014
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www.appliedballisticsllc.com
MV CAL, yes. Don’t CDM change the BC to 1.00? Unfortunately I don’t have my kestrel on me right now to try and see if the 1.00 will change
With a CDM their is no BC. When you use a BC you are essentially picking one of a dozen standards (Gsp, GL, G1.......) then you are saying "my bullet performs at this percentage of the standard I chose, so you should adjust....).

When you use a CDM instead of using a BC and the Drag Model of a standard, you are using the Drag Model of the actual bullet as measured in flight.

BC changes to 1 because you are comparing the bullet to itself, and not to another bullet so it is being zeroed out. (when you multiple something by 1 you get itself).
 
Feb 20, 2013
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This is incorrect information. At least on our systems. You can do a MV Cal, or a Ballistics Calibration on any CDM.
But in doing so, you are not actually tweaking the CDM itself, just the usual truing we all are aware of, while the original question is about tweaking the CDM, unless I got it wrong.
 
Apr 24, 2017
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But in doing so, you are not actually tweaking the CDM itself, just the usual truing we all are aware of, while the original question is about tweaking the CDM, unless I got it wrong.
Technically speaking... a CDM by itself is not “adjustable” because it’s is not a BC.

(example: If the shooter is shooting a Lapua 136 Scenar-L and uses a Lapua 136 Scenar-L CDM supplied by a particular Vendor. The shooter is comparing the performance of His/Her Lapua 136 Scenar-L to another Lapua 136 Scenar-L supplied by the vendor shot from that Vendors’ test equipment. NOT a “G-Standard-Projectile”)

If the question is “How Do I adjust the trajectory output for the solver if it needs fine tuning?”

Then the shooter would use whatever tools the vendor has implemented to do the fine tuning

Applied Ballistics would adjust MV or use the DSF feature depending where the trajectory needs adjusting

Honrady 4DOF would adjust the Axial Form Factor

Lapua Ballistic 6DOF app doesn’t support a “drag-variable” adjustment so the shooter would have to manually adjust MV to adjust the trajectory

(This presupposes that the shooter did their due diligence and followed the vendors’ pre-requisite checklist/procedures to rule out CWAJ in their zero. Shooting Azimuth, Scope tracking errors... etc in order for the vendors' tools to remain a fine adjustment rather than a gross adjustment)
 
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Feb 20, 2013
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Technically speaking... a CDM by itself is not “adjustable” because it’s is not a BC.

(example: If the shooter is shooting a Lapua 136 Scenar-L and uses a Lapua 136 Scenar-L CDM supplied by a particular Vendor. The shooter is comparing the performance of His/Her Lapua 136 Scenar-L to another Lapua 136 Scenar-L supplied by the vendor shot from that Vendors’ test equipment. NOT a “G-Standard-Projectile”)

If the question is “How Do I adjust the trajectory output for the solver if it needs fine tuning?”

Then the shooter would use whatever tools the vendor has implemented to do the fine tuning

Applied Ballistics would adjust MV or use the DSF feature depending where the trajectory needs adjusting

Honrady 4DOF would adjust the Axial Form Factor

Lapua Ballistic 6DOF app doesn’t support a “drag-variable” adjustment so the shooter would have to manually adjust MV to adjust the trajectory

(This presupposes that the shooter did their due diligence and followed the vendors’ pre-requisite checklist/procedures to rule out CWAJ in their zero. Shooting Azimuth, Scope tracking errors... etc in order for the vendors' tools to remain a fine adjustment rather than a gross adjustment)
I think it all comes down to what the OP really meant in his question about the CDMs.
Actually you can tweak the "drag curve" in Hornady 4DOF, Coldbore and FFS. How we adjust the trajectory is an altogether different scenario, where the usual truing ways come in. It doesn't matter if the drag curve is not a BC, because you can always change its form, at least in the mentioned software.
 
Likes: Kobyashi72
Feb 7, 2013
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Does the wind speed and direction need to be recorded in the ballistics app/software when truing the speed and the bc? Thanks.
If it is windy at all, I do NOT use it for my final truing number. If you do your base wind will always be in your predictions.

Unfortunately, to work BC correctly you need to work around image displacement and wind. It might mean the day you plan on “truing” doesn’t work.
 
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Likes: LastShot300
Apr 24, 2017
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If it is windy at all, I do NOT use it for my final truing number. If you do your base wind will always be in your predictions.

Unfortunately, to work BC correctly you need to work around image displacement and wind. It might mean the day you plan on “truing” doesn’t work.
Could you clarify what you mean when you say "If you do your base wind will always be in your predictions."?
 

Sogan

Sergeant
Jun 11, 2013
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Could you clarify what you mean when you say "If you do your base wind will always be in your predictions."?
Wind depending on the direction could influence your bullet up or down. If you true on a windy day then your numbers could be slightly off when you shoot another day with different wind speed or direction.
 
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Apr 24, 2017
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Wind depending on the direction could influence your bullet up or down. If you true on a windy day then your numbers could be slightly off when you shoot another day with different wind speed or direction.
The solver (presuming it supports AJ) would be accounting for that when the shooter inputs the wind speed and direction along with Latitude Azimuth and SD in order to isolate the secondary effects from being adjusted into the MV/BC.

If those inputs are left blank or turned off the solver will interpret the recorded drop that's being used to true the algorithm as being entirely the result of gravity instead of isolating the gravity component of the drop data from the secondary effects that were present in the environment when the drop data was recorded.
 
Feb 7, 2013
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The solver (presuming it supports AJ) would be accounting for that when the shooter inputs the wind speed and direction along with Latitude Azimuth and SD in order to isolate the secondary effects from being adjusted into the MV/BC.

If those inputs are left blank or turned off the solver will interpret the recorded drop that's being used to true the algorithm as being entirely the result of gravity instead of isolating the gravity component of the drop data from the secondary effects that were present in the environment when the drop data was recorded.
Let’s make this super simple-

Something I’ve seen, done over thousands of rounds and years of ELR shooting, is needing to really bend curves, or even use two profiles because the curve fit was to extreme.

Optical disturbances and high winds are almost impossible to estimate and cause very large result swings.

We see the effect, input the results. But because we do not have the actual optical or absolute wind data our inputs are flawed.

Just make sure to do your final tuning under ideal conditions..
 
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Skookum

Flattus Domini
May 6, 2017
1,007
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Your mom's
Let’s make this super simple-

Something I’ve seen, done over thousands of rounds and years of ELR shooting, is needing to really bend curves, or even use two profiles because the curve fit was to extreme.

Optical disturbances and high winds are almost impossible to estimate and cause very large result swings.

We see the effect, input the results. But because we do not have the actual optical or absolute wind data our inputs are flawed.

Just make sure to do your final tuning under ideal conditions..
I was out shooting at 2,400 yards just a couple of weeks ago and had a common experience that I think illustrates your point.

I had gathered dope on this load at 60 degrees F in this exact location in heavy overcast and in winds that were from 1130 oclock at less than 3mph. There couldn't have been better conditions.

I go out again on this day, and the only difference (same batch of ammo, same temp, same wind) is that the sun is out and rising over the mountain to my 10 oclock. My group was 0.5MILS low and 1 MIL right.
 
Apr 24, 2017
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Let’s make this super simple-

Something I’ve seen, done over thousands of rounds and years of ELR shooting, is needing to really bend curves, or even use two profiles because the curve fit was to extreme.

Optical disturbances and high winds are almost impossible to estimate and cause very large result swings.

We see the effect, input the results. But because we do not have the actual optical or absolute wind data our inputs are flawed.

Just make sure to do your final tuning under ideal conditions..
Thanks for clarifying. That makes more sense now
 
Apr 16, 2014
903
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Texas
www.appliedballisticsllc.com
When using a DSF you are essentially tweaking the Drag Curve. But you are doing it in a more advanced manner. You are adjusting the prediction at a specific Mach Number. This means the adjustments will carry over in all conditions. Bullet models are built off Mach/CD tables anyways, so this allows the prediction to be adjusted at a specific point, or points (up to 6).

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